Although the famous double helix of DNA is widely recognized as the biochemical lynchpin of organic growth and development, it also turns out to be a handy tool for managing enzymatic activities with entirely different outcomes.

About four years ago, University of Waterloo chemistry professor Juewen Liu began exploring the potential of DNA as a means of detecting new antibiotic compounds. This work built on the discovery in 1994 that short segments of this naturally occurring molecule could be isolated to form artificial enzymes with catalytic properties. Since then a variety of these DNAzymes have been synthesized. Not only could they help catalyse key reactions, they could also be used as probes to detect cofactors — organic molecules that help enzymes do their job — or other interesting biomolecules, such as antibiotics. 

Although this approach did not work well in the search for drug candidates, some of Liu’s students became interested in the fact that, in some cases, the catalytic action of these enzymes depended on metal ions, including lead, cadmium, mercury and various lanthanide elements. When a fluorophore is attached to a DNA strand, the resulting emission that signals the presence of such metallic ions serves as a practical molecular biosensor.

For Liu, who is a member of Waterloo’s Water Institute — a unique research-based graduate program jointly offered by 10 departments across the Faculties of Arts, Engineering, Environment, Mathematics and Science — this capability has become an attractive platform for determining heavy metal contamination in drinking water. He contrasts the technique with more standard water analysis technology, such as inductively coupled plasma mass spectrometry. ICP-MS is a comparatively expensive way to look for metals in a sample, Liu says, and the result indicates the total amount of a metal present as opposed to the proportion that might pose a health hazard. “Our sensor detects the free, bioavailable species. We would like to use this method in portable detectors that could be used on-site at a low cost, providing complementary information to the current technologies.”